#nullable enable

using System;
using System.Collections.Generic;
using System.Linq;
using Cysharp.Threading.Tasks;

namespace ShrinkApp;

[AttributeUsage(AttributeTargets.Class, Inherited = false, AllowMultiple = false)]
public sealed class ShrinkAppModuleInstallerAttribute : Attribute { }

public interface IShrinkAppModuleInstaller
{
    string ModuleId { get; }
    int Order { get; }
    IReadOnlyList<string> DependsOn { get; }
    void RegisterServices(ShrinkAppContext context);
    UniTask InitializeAsync(ShrinkAppContext context);
}

public interface IShrinkAppModuleShutdown
{
    UniTask ShutdownAsync(ShrinkAppContext context);
}

public sealed class ShrinkAppSettings
{
    public bool VerboseLogging { get; set; }
    public string[] DisabledModuleIds { get; set; } = Array.Empty<string>();
}

public sealed class ShrinkAppServices
{
    private readonly Dictionary<Type, object> _services = new();
    public void Register<T>(T service) where T : class => _services[typeof(T)] = service ?? throw new ArgumentNullException(nameof(service));
    public bool TryGet<T>(out T? service) where T : class
    {
        service = _services.TryGetValue(typeof(T), out var value) ? value as T : null;
        return service != null;
    }
    public T GetRequired<T>() where T : class => TryGet<T>(out var value) ? value! : throw new InvalidOperationException($"Required service is not registered: {typeof(T).FullName}");
    public bool TryUnregister<T>(T service) where T : class => _services.TryGetValue(typeof(T), out var value) && ReferenceEquals(value, service) && _services.Remove(typeof(T));
}

public sealed class ShrinkAppContext
{
    public ShrinkAppContext(object? host, ShrinkAppSettings settings, ShrinkAppServices services)
    {
        Host = host;
        Settings = settings ?? throw new ArgumentNullException(nameof(settings));
        Services = services ?? throw new ArgumentNullException(nameof(services));
    }
    public object? Host { get; }
    public ShrinkAppSettings Settings { get; }
    public ShrinkAppServices Services { get; }
    public static ShrinkAppContext CreateStandalone(ShrinkAppServices services, ShrinkAppSettings? settings = null) => new(null, settings ?? new ShrinkAppSettings(), services);
}

public sealed class ShrinkAppRuntime
{
    private readonly List<IShrinkAppModuleInstaller> _started = new();
    public ShrinkAppRuntime(object? host = null, ShrinkAppSettings? settings = null, ShrinkAppServices? services = null)
    {
        Context = new ShrinkAppContext(host, settings ?? new ShrinkAppSettings(), services ?? new ShrinkAppServices());
    }
    public ShrinkAppContext Context { get; }
    public bool IsRunning { get; private set; }
    public IReadOnlyList<string> StartedModules => _started.Select(item => item.ModuleId).ToArray();

    public async UniTask StartAsync()
    {
        if (IsRunning) return;
        var installers = Sort(CreateInstallers(), Context.Settings.DisabledModuleIds);
        try
        {
            foreach (var installer in installers) installer.RegisterServices(Context);
            foreach (var installer in installers)
            {
                await installer.InitializeAsync(Context);
                _started.Add(installer);
            }
            IsRunning = true;
        }
        catch
        {
            await ShutdownStartedAsync();
            throw;
        }
    }

    public async UniTask ShutdownAsync()
    {
        await ShutdownStartedAsync();
        IsRunning = false;
    }

    private async UniTask ShutdownStartedAsync()
    {
        for (var index = _started.Count - 1; index >= 0; index--)
            if (_started[index] is IShrinkAppModuleShutdown shutdown) await shutdown.ShutdownAsync(Context);
        _started.Clear();
    }

    private static IReadOnlyList<IShrinkAppModuleInstaller> CreateInstallers() =>
        ShrinkAppInstallers.GetDiscoveredInstallerTypes().Select(type =>
            Activator.CreateInstance(type) as IShrinkAppModuleInstaller ?? throw new InvalidOperationException($"Failed to create installer: {type.FullName}"))
            .ToArray();

    private static IReadOnlyList<IShrinkAppModuleInstaller> Sort(IEnumerable<IShrinkAppModuleInstaller> source, IEnumerable<string> disabledIds)
    {
        var disabled = new HashSet<string>(disabledIds ?? Array.Empty<string>(), StringComparer.OrdinalIgnoreCase);
        var byId = source.Where(item => !disabled.Contains(item.ModuleId)).ToDictionary(item => item.ModuleId, StringComparer.OrdinalIgnoreCase);
        var states = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);
        var result = new List<IShrinkAppModuleInstaller>();
        foreach (var installer in byId.Values.OrderBy(item => item.Order).ThenBy(item => item.ModuleId, StringComparer.OrdinalIgnoreCase))
            Visit(installer, byId, states, result);
        return result;
    }

    private static void Visit(IShrinkAppModuleInstaller installer, IReadOnlyDictionary<string, IShrinkAppModuleInstaller> byId,
        IDictionary<string, int> states, ICollection<IShrinkAppModuleInstaller> result)
    {
        var state = states.TryGetValue(installer.ModuleId, out var value) ? value : 0;
        if (state == 2) return;
        if (state == 1) throw new InvalidOperationException($"Circular installer dependency: {installer.ModuleId}");
        states[installer.ModuleId] = 1;
        foreach (var dependencyId in installer.DependsOn ?? Array.Empty<string>())
        {
            if (!byId.TryGetValue(dependencyId, out var dependency))
                throw new InvalidOperationException($"Installer dependency missing. Module={installer.ModuleId}, DependsOn={dependencyId}");
            Visit(dependency, byId, states, result);
        }
        states[installer.ModuleId] = 2;
        result.Add(installer);
    }
}